Electroacoustic device



5 Sheets-Sheet 1 SOURCE.

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Mmh i8, 1930. J, P, MINTON ET AL ELECTRQACOUSTIC DEVICE Filed Aug. l5,1924 March 18, 1930. J. P. MaNToN ET AL S ELECTROACOUSTIC DEVICE FiledAug. l5, 1924 3 Sheets-Sheet 2 INVENToRs JOHN aRasToN mm1-0N Asn HAMames. v

/L fm A 55 E5 ORNEY March 18,- 1930. J, P, MINTON El' AL ELECTROACOUSTIC DEVI CE File'd Aug. l5a S1924 3 Sheets-Sheet 3 INVENTORS JOHN PRESTONMINTQN ABRAHM l BY A SRNGEL.

Patented Mar. 18, 1930 LUNITED STATES PATEN'n OFFICE JOHN PRESTONHINTON, OF WHITE PLAINS, AND ABRAHAM S. RINGEL, OF BROOKLYN, NEW YORK,ASSIGNORS TO RADIO CORPORATION OF AMERICA, A CORPORATION OF DELAWAREELECTROACOUSTIC DEVICE Appiieuon 111m August 15, 1924. serial No.732,153.

'Our invention relates to acoustic devices and particularly toelectro-acoustic devices of the so-called loud speaker type. Ourinvention further relates to sound reproduction and ampliicationmethods.

One of the principal objects of our invention is the provision of anelectro-acoustic device possessing the following charactertially maximumuniform amplification over` a wide range of frequencies with theemployment of a comparatively small amount of power.

4 Tonal quality control. 5 Low manufacturing costs. 6) Constructionalfeatures im arting rigidity to the device resultin in t e substantialelimination of undesirable vibrations.

Other objects and advantages of our .invention will be apparent from thefollowmg description taken 1n connection with the accompanying drawings,in which: I

F 1g. 1 is a perspective view of a cablnet and a preferred' embodimentof our*y loud speaker mounted therein.

Fig. 2 isa combined perspective view and schematic dia ram ofconnections of a preferred embodlment of our invention.

Fig. 3 is a front elevation partly in section. Fig. 4 is a sideelevation of the horns. Fig. 5 is a top plan view of the horns.' Fig. 6is a top plan View partly in section of thehorns with certain partsbroken away ,to more clearly disclose their structural relationship. p

Fig. 7 is a plan view of a diaphragm actuating device.

A preferred embodiment of ourl loud speaker comprises twolelectro-acoustic units A and B of different sizes and possessingdifferentl electrical and Aacoustical character- ,istics The unit A issubstantially resonant `to the lower range of audible frequencies whilethe unit B is substantially resonant to the upper range of audible freuencies resulting in the substantially uni orm reproduction andamplification of sound over a much wider range of frequencies than isattainable with a single unit.

The unit A which is the larger of the two, comprises an exponential horn1 and an electro-magnetic sound reproducer 2.

The horn 1, which is the longer of the two and which opens up at a slowrate, comprises an intermediate vertical tapering portion3 ofquadrilateral cross section, terminating at its upper end in an openhorizontal flaring portion 4 communicating with o nings 5 in cabinet 6and at its lower end 1n a securing portion 7 of cylindrical crosssection as shown.

The horn 1 may be appropriately secured to certainV of the innersurfaces of the cabinet 6 by means of substantially L-shaped brackets 8;Y

The unit B, which is the smaller of the two, comprises a straightexponential horn 10 and an electro-magnetic sound reproducer 11.

The horn 10, which is the shorter of the `two and opens up ata morerapid rate than horn 1, comprises a straight intermediate horizontaltapering portion 12 of quadrilat- 80 eral cross section terminating atone end in an open horizontal flaring portion 13 and at vthe other endin a securing portion 14 of cylindrical cross section as s own. i

The tapering portion 12 is inserted thru an opening 15 in one of thesides of the horizontal Haring portion 4 of horn 1, the opening ofthe'horizontal flaring portion 13 coinable metal stampings, which may besoldered,

' brazed or welded together at their' edges.

The metal em loyed should be of such a character and t ickness as `notto vibrate.

As the two electro-magnetic sound reproducers 2 and 11- are similarl'except as to size, the magnetic dia hragm of 2 being of greaterdiameter than -t at of ll-and the actuating coils of 2 having a largernumber of turns and consequently a greater inductance than those of 11,a description of onewill suffice for both.

The electro-magnetic sound reproducer 2 comprises an enclosingcylindrical casing 18 open at its lower end and closed at its upper endby an integral closure member 19 terminating in a nipple 2O arranged tobe frictionally engaged on its outside cylindrical surface by the lowersecuring portion 7 of horn 1 as shown. The horn 10 is similarly securedto the sound reproducer 11.

A peripheral shoulder 21 is integral with the enclosing casing 18 and iscontained there- Y in. The low frequency diaphragm 22, constructed ofappropriate diaphragm material, is spaced away from the closure member19, resting against the outer surface of the shoul- -4 der 21 and isheld in engagement therewith by means of a clamping ring 23 and screws24 passing through registering holes in the periphery of the diaphragmand ring, the said screws being threaded in the body of shoulder 21. y

The lower end of the casing 18 is internally threaded for the-receptionof a closure member 25 made of-some suitable non-magnetic material andhaving an integral upwardly extending flange 26 externally threaded forengagement with the internally threaded lower end of the enclosingcasing 18.

The diaphragm actuatingf'mechanism (of which Fig. 7 is a plan view)comprises a substantially U-shaped permanent magnet 27 suitably securedto the inner surface of the closure member 25. The freeends 28 and 29 ofthe permanent magnet are vjoined together arecomposedofa plurality ofsimilar lami- .nations united together, have two integral pole pieces32, 32 extending toward'the diaphragm 22. Magnetizing coils 33, 33 aremounted around said pole pieces and held in place thereon by means ofsuitable insulated washers 34, 34. The operation of the dia-- phragmactuating mechanism, being well known in the art, requires nodescription here. The leads from the coils 33, 33 and 33,', 33 may beconnected to. insulated terminals 35,

' 35 and 35', 35 respectively mounted in the closure members 25 and 25respectivelyfas shown. g

Independent control of the volume of sound emanating from the units maybe effected by independently screwing the closure members 25 and 25clockwise or counterclockwise to thereby vary the spacing between thepoles 32 and 32 and the diapliragms 22 and 22 respectively. This resultsin tonal quality control.

The coils of the electro-magneticsound reproducers 2 and 11 areeonnecte'd in series across the output terminals of the"source ofreceived signals assliown in Fig. 2. A con .denser 36 is connectedacross the coils of the reproducer 2 for a purpose to be hereinafterdescribed.

The horn 1 and the diaphragm 22 of the sound reproducer 2 are arrangedto be substantially resonant tothe lower band of audible frequencieswhich are to-'be reproduced and amplified. The horn 10 and the diaphragm22 of the sound reproducer 11 are arranged topbe substantially resonantto the upper band of audible frequencies which ar to be reproduced andamplified.

The coils of sound reproducers 2 and 11 and the condenser -36 are soarranged as to result in a substantially uniform impedance substantiallyequal to the impedance of the source of received signals over theentire'range of audible frequencies to be reproduced and amplified.Substantially maximum uniform reproduction and amplification of thefrequencies to be reproduced and amplified over the entire range ofaudible frequencies with a minimum amount of power thereby results, orconversely, a maximum and substantially uniform volume of sound resultsover the entire range of audible frequencies with la given amount ofavailable power.

The condenser 36 together with the comparatively large inductance of thecoilsv33, 33

prevents the higher band of frequencies from influencing the operationof the sound reproducer 2.- 'I he 4coils 33', 33', possessingcomparativel small inductance, arel readily influenced by the upper bandof frequencies while the comparatively small diaphragm 22 of the soundreproducer 11 is substantially non-responsive to the lower band offrequencies. The substantial elimination of the effects of interferingfrequencies is therefore effected.

1. In combination, a plurality of intersecting sound amplifying hornseach substantially resonant to a different portion of the audible rangeof frequencies, and an electroacoustic device attached to eachof saidhorns. 2. In combination, a pair of intersecting stantially resonant tothe upperportion of the` audible. spectrum, the other of which is substantially resonant to the lower portion of the audible spectrum,- and apair of electro-acoustic `devices attached to, and having similarfrequency characteristics to, the horns.

' 3. A pair of intersecting sound amplifying Asound amplifying horns oneof which is sub horns, rigidly attached together at their vline ofintersection and at points along the pneripheries of their outlets, eachof said horns being substantially resonant to a different portion of theaudible range of frequencies, and an electro-acoustic device attached toeach of the horns, leach device having frequency characteristics similarto the horn to which it is attached. i

4. In an apparatus for the transformation of electrical undulations intosound vibrations, the combination of a plurality of electro-acousticdevices each substantially resonant to a predetermined portionof theaudi ble frequency spectrum, each having independent means for varyingthe amplitude of vibration of a diaphragm in each of saidelectro-acoustic devices, said devices having intersecting soundamplifying horns" rigidly united together at their line of intersectionand partly along the peripheries of their outlets.

5. In an apparatus for the transformation of electrical undulations intosound vibrations, a pair of electro-acoustic devices one of which issubstantially resonant to the lower range of the audible spectrum andthe other of which is'substantiall'y resonant to the upy per range ofthe audible spectrum, each of said devices having independent Ameans forvarying the amplitude ofvvibration of a diaphragm in each of them, saiddevices having intersecting sound amplifying horns rigidly unitedtogether at their line of intersection and, in substantially one plane,partly along the peripheries of their outlets.

6. In combination, apair of horns, one of which intersects and passesthrough at least one part of the other horn,`each of said horns beingresonant to a different portion of the audio frequency spectrum, and aseparate source of sound energy for each horn.

7. In combination, a pair of intersecting horns, one'of said hornsadapted for amplifying frequencies of the lower portion of the audiofrequency spectrum, the other horn being relatively short with referenceto said first described horn, said other horn being adapted foramplifying the frequencies of the upper portion of the audio frequencySpectrum, and a separate source of sound energy v for each horn.

8. A pair of intersecting sound amplifying horns attached together attheir intersection and at their outlets.

9. A pair of sound amplifying different' size and shapeintersectingintermediate their inlets and outlets, the outlets 'of the horns lyingin substantially the same plane and united together at a plurality ofpoints in said plane, the intermediate portions of the horns beingrigidly fastened together at their intersection. A

`10. In combination, a plurality of interseating sound amplifying horns,each sublhorns of' stantially, resonant to a different portion of theaudible range of frequencies, an electroacoustic device attached'to eachof said horns, and said horns being attached together at their outlets.

11. vIn combination, a plurality of intersectv

